Alpha Lacertae

Alpha Lacertae, Latinised from α Lacertae, also named Stellio,^[9] is a single^[10] white-hued star in the constellation of Lacerta,^[8] located 103^[1] light-years from the Sun. It is the brightest star in Lacerta with an apparent visual magnitude of 3.76.^[2] The star is moving closer to the Earth with a heliocentric radial velocity of −4.5 km/s.^[5]

α Lacertae

α Lacertae in optical light
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Lacerta
Right ascension	22h 31m 17.50131s[1]
Declination	+50° 16′ 56.9682″[1]
Apparent magnitude (V)	3.76[2]
Characteristics
Spectral type	A1 V[3]
U−B color index	0.00[4]
B−V color index	0.031±0.003[2]
R−I color index	−0.03[4]
Astrometry
Radial velocity (Rv)	−4.5±0.9[5] km/s
Proper motion (μ)	RA: 137.51[1] mas/yr Dec.: 17.01[1] mas/yr
Parallax (π)	31.79±0.12 mas[1]
Distance	102.6 ± 0.4 ly (31.5 ± 0.1 pc)
Absolute magnitude (MV)	1.27[2]
Details[6]
Mass	2.194 M☉
Radius	2.1432±0.0737 R☉
Luminosity	27.6750±0.2138 L☉
Surface gravity (log g)	4.27±0.14[7] cgs
Temperature	9,050±157 K
Rotational velocity (v sin i)	128[7] km/s
Age	400 Myr
Other designations
Stellio, α Lac, 7 Lac, BD+49°3875, FK5 848, GC 31471, HD 213558, HIP 111169, HR 8585, SAO 34542, ADS 16021 A, CCDM J22313+5017A, WDS J22139+3943[8]
Database references
SIMBAD	data

This is an ordinary A-type main-sequence star with a stellar classification of A1 V,^[3] which indicates it is generating energy through hydrogen fusion at its core. It is around 400^[6] million years old with a relatively high rate of spin, showing a projected rotational velocity of 128 km/s.^[7] The star has 2.2 times the mass of the Sun and 2.1 times the Sun's radius. It is radiating 28 times the Sun's luminosity from its photosphere at an effective temperature of 9,050 K.^[6]

Alpha Lacertae has a visual companion, CCDM J22313+5017B, of spectral type A and apparent visual magnitude 11.8, approximately 36 arcseconds away.^[11] The companion is optical, a chance line-of-sight coincidence.^[4]

Naming

Alpha Lacertae is the Bayer designation for this star; it has the Flamsteed designation 7 Lacertae. In Chinese, 螣蛇 (Téng Shé), meaning Flying Serpent, refers to an asterism consisting of α Lacertae, 4 Lacertae, π² Cygni, π¹ Cygni, HD 206267, ε Cephei, β Lacertae, σ Cassiopeiae, ρ Cassiopeiae, τ Cassiopeiae, AR Cassiopeiae, 9 Lacertae, 3 Andromedae, 7 Andromedae, 8 Andromedae, λ Andromedae, κ Andromedae, ι Andromedae, and ψ Andromedae. Consequently, the Chinese name for α Lacertae itself is 螣蛇一 (Téng Shé yī, English: the First Star of Flying Serpent).^[12]

The IAU Working Group on Star Names approved the name Stellio for this star on 29 August 2024 and it is now so entered in the IAU Catalog of Star Names.^[9] Stellio is an obsolete historical name for the constellation Lacerta, named after the lizard Laudakia stellio, the starred agama or stellion.^[13]